Growth hormone is a major participant in the control of several complex physiologic processes, including growth and metabolism. Growth hormone is known to have a number of effects on metabolic processes, e.g., stimulation of protein synthesis and free fatty acid mobilization and to cause a switch in energy metabolism from carbohydrate to fatty acid metabolism. Deficiency in growth hormone can result in a number of severe medical disorders, e.g., dwarfism.
The release of growth hormone from the pituitary is controlled, directly or indirectly, by number of hormones and neurotransmitters. Growth hormone release can be stimulated by growth hormone releasing hormone (GHRH) and inhibited by somatostatin. In both cases the hormones are released from the hypothalamus but their action is mediated primarily via specific receptors located in the pituitary. Other compounds which stimulate the release of growth hormone from the pituitary have also been described. For example, arginine, L-3,4-dihydroxyphenylalanine (1-Dopa), glucagon, vasopressin, PACAP (pituitary adenylyl cyclase activating peptide), muscarinic receptor agonists and a synthetic hexapeptide, GHRP (growth hormone releasing peptide) release endogenous growth hormone either by a direct effect on the pituitary or by affecting the release of GHRH and/or somatostatin from the hypothalamus.
The use of certain compounds for increasing the levels of growth hormone in mammals has previously been proposed. For example, U.S. Pat. Nos. 6,303,620 and 6,576,648 (the entire contents of which are incorporated herein by reference), disclose a compound: (3R)-1-(2-methylalanyl-D-tryptophyl)-3-(phenylmethyl)-3-piperidinecarboxylic acid 1,2,2-trimethylhydrazide, having the following chemical structure:
which acts directly on the pituitary cells under normal experimental conditions in vitro to release growth hormone therefrom. This growth hormone releasing compound can be utilized in vitro as a unique research tool for understanding, inter alia, how growth hormone secretion is regulated at the pituitary level. Moreover, this growth hormone releasing compound can also be administered in vivo to a mammal to increase endogenous growth hormone release.